It is imperative for certain products to be kept below a specific temperature, for example perishable foods and pharmaceuticals. It has long been a problem to track the temperatures of such products and many methods and devices have been tried, but there is still room for improvement.
Currently, there are irreversible indicators available that undergo a permanent color change when exposed to a temperature excursion. Also, there are electronic temperature monitors that can record the temperature to which a product has been exposed over a specified time interval, i.e., time-temperature indicators. These electronic temperature monitors are battery powered, which is a limitation because the battery could die or fail and data may not be collected or may be lost.
There is a need for indicators that do not use a battery, provide self-verification, and have more than one mode of indicating a temperature event.